1. Field of the Invention
The present invention relates to high voltage insulated cable terminations, and more particularly to such type cable terminations intended to be connected to a pressure-gas-insulated conductor.
2. Prior Art
To obtain a voltage-grading termination on a highvoltage cable with an insulation of cross-linked polyethylene (PEX), there is often used some form of a rubber stress cone with a conductive external coating. The cone reduces the electric field strength around the cable end and keeps the field strength gradient along the cable insulation sufficiently low to avoid partial discharges, and thus the risk of breakdown in the insulating medium which surrounds the cable termination. Normally, at low voltages this insulating medium consists of air, thereby providing simple and inexpensive terminations which are easy to handle.
To obtain reasonable dimensions, PEX cables designed for some twenty or thirty kV and higher operating voltages are generally provided with a fluid-insulated termination in an electrically insulating enclosure of plastic or a ceramic material. Such a construction entails costs for the fluid and its insulating enclosure as well as expansion space for the thermal expansion of the insulating fluid. Because of this fact some of the advantages of the PEX cable construction, such as low weight and flexibility and completely dry insulation, are lost. With the enclosure and its accessories a fluid-insulated termination is also rather bulky, which is a considerable disadvantage when connecting PEX cables to switch gear systems insulated with sulphur hexafluoride SF.sub.6 and which require small dimensions.